1. Field of the Invention
The present invention relates to a melting apparatus for melting and slagging a waste water treatment sludge, an ash or dust discharged from an incinerating apparatus, or the like and, more particularly, relates to a melting apparatus comprising a structure for effectively collecting low boiling point dust apt to circulate in the dust collecting path.
2. Description of the Prior Art
In arrangements for incinerating and treating a waste to be treated, it is widely used, for the purpose of solidifying an incinerated residue and collected dust, that a melting furnace is provided in the post process of an incinerating furnace, wherein the incinerated residue and the collected dust are melted and slagged, and then the melted slag is cooled and solidified to be discharged. A waste water treatment sludge is directly melted in a melting furnace to produce a melted slag which then is cooled and solidified to be discharged.
FIG. 1 shows a flow diagram of a conventional melting apparatus for performing the above described melting and treatment. After collected waste 1 temporarily is stored in a reservoir pit, the waste 1 is incinerated in an incinerating furace. An incinerated residue 2 such as ash or non-combustible material, and exhaust gas 3 are discharged from the incinerating furnace. Of these, the incinerating residue 2 is introduced into a melting furnace, the temperature of which is raised to a predetermined temperature, and is melted and slagged, and then the melted slag is cooled and solidified to be discharged as a solid slag 7 out of of the system. On the other hand, the exhaust gas 3 is passed to an exhaust gas cooling portion A (for example, a water sprinkling cooler apparatus) so that the gas 3 is cooled, and then, after the dust included in the exhaust gas is removed in a dust collecting portion A, the gas is discharged to the exterior. The dust 4 collected in the dust collecting portion A is introduced into the melting furnace wherein the dust 4 is melted and slagged together with the incinerated residue 2. In addition, an exhaust gas 5 generated when the incinerated residue 2 and the collected dust 4 are melted in the melting furnace, is introduced into a heat exchanger and cooled therein, and then, is through a line 6 to be joined with the exhaust gas 3 from said incinerating furnace through a line 6 to be supplied to the dust collecting portion A in which the dust is again collected.
However, the chloride or dust generated or collected in the above described melting furnace contains components such as ZnCl.sub.2, PbCl.sub.2, CdCl.sub.2, KCl, NaCl and FeCl.sub.2, having a lower boiling point than the temperature within the melting furnace. These low boiling point dusts are gasified in the melting furnace and thus discharged with the exhaust gas and the like. Therefore, such dust can not be solidified. If such gasified component having a low boiling point is cooled in a heat exchanger, the component is again solidified to become dust and is collected in the dust collecting point A. Thus, the collected dust is again introduced into the melting furnace. However, since the internal temperature in the melting furnace is higher than the boiling point of the low boiling point component, the low boiling point components are again gasified to circulate in the system. Thus, such low boiling point components always continue to circulate in the collecting system and hence are not discharged to the exterior of the system. Therefore, while such kind of melting apparatus continues to be driven for a longer time period, such low boiling point dust is stored in the collecting system and a considerable amount thereof is deposited on an inner surface of each tube of a heat exchanger through which the exhaust gas 5 from the melting furnace flows. Such deposits block the heat exchanger tubes or cause a failure of the tube and heat exchanger.
Then, the present inventor has proposed a structure for overcoming such a problem in his prior filed Japanese patent application No. 100119/1982 which has not been laid open for public inspection. In that application, a structure is disclosed wherein a separate dust collecting portion is provided in an exhaust gas line 6 of the melting furnace, in which dust collecting portion the low boiling point dust is collected and is introduced into a separately designed melting furnace having a lower furnace temperature in which the low boiling point dust is melted and slagged and is discharged to the exterior of the system.
However, even in such an improved melting apparatus, there are some problems because the structure is relatively complicated and the operation of the re-melting furnace is expensive.